Rotational molding apparatus

ABSTRACT

A rotational molding apparatus is provided in which a hollow spherical member is supported on rollers, and in which the rollers are controlled to cause the spherical member to turn on an infinite number of axes. One or more molding cavities are supported within the spherical member and which rotate therewith to carry out rotational molding operations.

United States Patent Clay [54] ROTATIONAL MOLDING APPARATUS [72]Inventor: Robert A. Clay, 1306 Logan Street,

Costa Mesa, Calif. 92626 [22] Filed: Nov. 9, 1970 211 Appl. No.1 87,933

[52] US. Cl. ..425/404, 425/429, 264/311 [51] Int. Cl. ..B29c 25/00,B29c 5/04 [58] Field of Search..... 1 8/26 RR; 264/311; 425/404,425/425, 429, 430, 433, 434

[56] References Cited UNITED STATES PATENTS 3,350,745 11/1967 Schott etal. ..l8/26 R 2,811,747 11/1957 Belz ..18/26 R 2,904,836 9/1959Jefferson et a1. ..I8/26 RR Nov. 28, 1972 2,946,092 7/1960 Yoder 18/26 R3,239,906 3/ 1 966 Ribot ..18/26 R X FOREIGN PATENTS OR APPLICATIONS39/15444 1964 Japan ..18/26 RR Primary Examiner-Robert I... Spicer, Jr.Attorney-Jessup & Beecher ABSTRACT A rotational molding apparatus isprovided in which a hollow spherical member is supported on rollers, andin which the rollers are controlled to cause the spherical member toturn on an infinite number of axes. One or more molding cavities aresupported within the spherical member and which rotate therewith tocarry out rotational molding operations.

8 Clains, 5 Drawing Figures SHEET 2 OF 3 PATENTEnnnvza I972 BACKGROUNDOF THE INVENTION Rotational molding apparatus is known in which amolding cavity is rotated at a low rotational speed. This speed issufficiently low so that the molten molding material is disposed at thebottom of the cavity, and a layer of the molding material is depositedon the wall of the cavity as the mold turns.

If the mold is turned on one axis, however, a single annular layer ofthe molding material is deposited around the inner surface of the mold.This means that the mold surface is not completely covered with themolding material. Therefore, if the molding material is to form auniform coating over the entire inner surface of the mold cavity, as isusually required, the mold must I be rotated on more than one axis.

In one known type of prior art rotational molding apparatus, the mold isrotated about two axes disposed at right angles to one another. Whenthis type of prior art apparatus is used, a number of orbital depositsof the molding material on the inner surface of the mold cavity areformed, and in most cases the spreading characteristics of the materialand the changing direction of the gravitational effect, enables themolding material to establish a continuous coating on the wall of themold cavity. However, such prior art apparatus, apart from being undulycomplex and expensive, has tendency to create non-uniform wallthicknesses of the object formed thereby.

In the prior art two axis, molding apparatus, the mold must be rotatedabout the axes at different rates, or only one orbital deposit will beformed on the wall of the cavity. If one axis is rotated faster than theother, the number of orbital deposits may be proportionally increased.Moreover, the greater the speed ratio between the two axes, the greateris the area of the cavity wall covered by the molding material. However,there are limits to the speeds at which molds for rotational molding maybe rotated, otherwise centrifugal forces are encountered which displacethe molten material at the bottom of the mold cavity.

tion of the molding material over the wall of the mold cavity so thatmolded objects of any desired uniform wall thickness may be formed inrelatively short processing times. Another objective is to provide sucha mold that lends itself to high production rotational moldingoperations.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevational view, partlyin section, showing molding apparatus constructed in accordance with oneembodiment of the invention;

FIG. 2 is an elevational view like FIG. 1, but with the apparatusrotated 90 about a vertical axis;

FIG. 3 is a side elevation of another embodiment in which a plurality ofspherical members are directed through an oven and cooling chamber for ahigh production operation; I

FIG. 4 is an end view of the apparatus of FIG. 3; and

FIG. 5 is a top plan view of the apparatus of FIG. 3.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT The molding apparatusshown in the drawing includes, for example, a base 10. A pair of shafts12 and 14 are rotatably supported in appropriate bearings 15 which, inturn, are mounted on suit able brackets 16 Another prior art rotationalmolding apparatus is one in which the mold is rotated around a singlehorizontal axis, and is angularly moved in a reciprocal manner about asecond axis which is orthogonally related to the horizontal axis.However, such a prior art molding apparatus also tends to produce anuneven coating of the molding material on the wall of the cavity, andespe-' cially at the parts of the cavity adjacent the rotational axis.

The rotational molding apparatus of the present invention as indicatedabove, includes one or more hollow spherical members supported onrollers, and which may be controlled so that each spherical memberturned about an infinite number of axes. The result is that the moldcavity mounted within the individual and 18. Frusto-conical shapedrollers 20 are keyed to the shafts 12 and 14 by any appropriate means,such as by set screws 22. A hollow spherical shaped member 24 issupported on the frusto-conical rollers 20, as shown. The shafts 22 aredriven by appropriate drive means such as an electric motor 30, areduction gearing 32, and an appropriate transmission system, includingpulleys 34 and 36 and a belt 38.

The elements 30-36 are used, for example, to drive the shaft 12 at aspeed, and in a direction determined, by an appropriate manuallyoperated control 40. it is to be understood that a similar drive meansmay be provided for the shaft 14, so that independent controls may beexerted on the shafts 12 and 14, which control the rate and direction ofrotation of the respective shafts, and of the rollers 20 mountedthereon.

The bearings 15 may be supported on appropriate slide members 40 and 42which, in turn, are supported on the respective brackets 16 and 18. Theslide members 40 and 42 may be under control of appropriate hydraulicactuators, such as the hydraulic actuator 44 in FIG. 2. The hydraulicactuators may be independently controlled, so as to cock the shafts 12and 14 to cause the respective rollers to assume any desired inclinationwithin the horizontal plane. As the inclination of the rollers ischanged, so is the axis around which the spherical member 24 is rotated.Therefore, by controlling the inclination of the rollers, the sphericalmember 24 may be made to actuate about any one of an infinite number ofaxis. Also, as mentioned above, the direction and speed of rotation ofthe spherical member may be controlled by manual or automaticmanipulation of appropriate controls, such as the control 40.

Therefore, a simple and inexpensive rotational molding apparatus isprovided, in which the desired rotation of one or more mold cavitiesmounted within the spherical member 24 may be easily and simplycontrolled, so

that the mold cavities are rotated at selected speeds of a mechanismillustrated in FIG. L The illustrated mechanism includes an upright post60, and an overhanging arm 62 pivoted to the upper end of the post 60means, for example, of a shaft 64. A hydraulic motor 66, or otherappropriate means, is coupled to the arm 62 and to the post 60 to turnthe arm 62 about the axis of rotation of the shaft 64. A suitablycontrolled electromagnet 68 is mounted on the end of the arm 62.

In order to remove the upper half of the spherical member 24, the magnet68 is energized, and the hydraulic motor 66 activated to turn the arm 62in a counterclockwise direction. The attraction of the magnet 68 to thesphere 24 causes the upper half of the sphere to be lifted clear of thelower half, so that the molding cavities may be exposed for loading andunloading purposes. I

An appropriateburner assembly 70 may be provided directly in the sphere24, and the assembly may include its own source of fuel, such as gas,together with an appropriate timer. The burner assembly 70 when ignited,provides the desired heat for the mold cavities. The spherical membermay incorporate a multiplicity of vent holes 72 which permit theproducts of combustion from the burner 70 to escape.

The actual molding dies, which form the mold cavitics, may be supportedin any appropriate means within the sphere 24. In addition, a hood 78may be provided around the apparatus, as shown in FIG. 2, and whichmounts a plurality of nozzles 80. Then, at the end of the moldingoperation, cooling water sprays may be directed over the sphere 24 andinto the vent holes 72 from the nozzles 80 so as to cool the mold dieswithin the sphere. The water sprays are initiated, for example, byturning on a valve 82.

The apparatus shown in FIGS. 3, 4 and 5, as mentioned above, constitutesa high production rotational molding apparatus in which a plurality ofspheres 100 are used, each of which may be similar to the sphere 24described above. The spheres 100 are supported'on a pair of spacedshafts 102 and 104 which are individually driven at controllable speedsby drive motors 106 and 108 through appropriate belt drives 110 and l ll, or their equivalent. The shafts, moreover, may be moved laterallytowards and away from one another to change the axis of rotation of thespheres supported thereon. The transverse motion of the shafts may beachieved, as shown in FIG. 5, by supporting the shafts in bearings 120and on rollers 122, which may be moved laterally across supporting bases124. The lateral adjustments of the shafts may be made by adjustablescrew mechanisms 126.

As the shafts 102 and 104 are driven at different speeds, the variousspheres 100 are caused to turn about a multiplicity of axes, and arealso caused to move, for example, from the left to the right in FIG. 3,

moved, they first pass through an ovel 1 12 where they are raised to therequired molding temperature, and

they are subsequently moved through a cooling,

chamber 114 where waterisprays or other means are used to cool themolds, as in the previous embodiment.

As the spheres are discharged from the chamber 114, and as shown in FIG.5, a gravity feed track 128 carries the spheres to a removal andrecharging area. The spheres are opened at the area and the moldedproducts removed from the internal molding dies 132. The molding diesare then again charged with molding material and the spheres are closedand transported to the entrance of the oven 122 by a track 134. Theresult of the use of the apparatus of FIGS. 3-5 i that high productionrotational molding may be achieved. As the spheres 100, for example,pass from the cooling chamber. 114, they move to the removal andrecharging area where the resulting molded products are removed. Then,the molding material is again inserted into the mold cavities in theindividual spheres, as mentioned, and the spheres are returned by, thetrack 134 back to the entrance of the oven 112 to be passed through theoven 1 12 and through cooling chamber 114. Y i

The invention provides, therefore, an improved rotational moldingapparatus which is constructed in order that a hollow spherical ball issupported on rotatable members,,such as rollers or shafts, so as to beeasily controllable for rotation about an infinite number of axes.Heating within the sphere for molding purposes may be provided, asdescribed, by means of an internal burner. Alternatively, and as alsodescribed, the sphere may be moved through a heating oven. As a furtheralternative, for example, the sphere may be placed in a bath of hot oiland rotated for heating purposes.

The rotation of the sphere about the infinite number of axes, asdescribed, provides for a uniform distribution of the molding materialover the inner wall of the mold cavity supported within the sphere. Asalso described, the use of the hollow spheres of the present invention,supported on appropriate shafts is advantageous in that it enablesheavier and larger molds to be used as compared with the prior artapparatus in which the molds aresuspended on the ends of rotating arms.Also, it enables the spheres to be used for high production rotationalmolding operations, by means of a plurality of such spheres transportedcontinuously through an oven and cooling chamber, such as describedherein.

It is apparent, therefore, that although particular embodiments of theinvention have been shown and described, modifications may be made. Itis intended to cover such modifications in the following claims.

Iclaim: 1

l. Rotational molding apparatus comprising: a base; roller meanscomprising first and second shafts rotatably supported on said base inspaced parallel relationship for rotation about respective horizontalaxes, and a plurality of conicalshaped members supported on said shafts;and a hollow spherical member freely supported on said roller means forrotation thereby about an infinite number of axes.

2. The rotational molding apparatus defined in claim 1, and whichincludes drive means coupled to said shafts for rotating said shafts andsaid conical-shaped members thereon at individually controllable speeds.

3. The rotational molding apparatus defined in claim 1, and whichincludes a burner assembly mounted in said hollow spherical member.

4 The rotational molding apparatus defined in claim 3, in which saidhollow spherical member has a multiplicity of vent holes formed therein.

5. The rotational molding apparatus defined in claim 1, and whichincludes a hood surrounding said hollow spherical member, and aplurality of nozzles mounted on said hood for directing coolant spraysonto said hollow spherical member.

6. The rotational molding apparatus defined in claim 1, in which saidroller means comprises first and second shafts rotatably supported onsaid base in spaced and parallel relationship for rotation aboutrespective horizontal axes; oven means surrounding said shafts along aparticular length thereof, said shafts causing said spherical member tomove through said oven means as it is rotated by said shafts.

7. The rotational molding apparatus defined in claim 6, and which alsoincludes a cooling chamber surrounding said shafts along a particularlength thereof, and in which said shafts cause said spherical membersubsequently to move through said cooling chamber after passing throughsaid oven means.

8. The rotational molding apparatus defined in claim 6, and whichincludes driven means coupled to said shafts for rotating said shafts atindividually controllable speeds.

1. Rotational molding apparatus comprising: a base; roller meanscomprising first and second shafts rotatably supported on said base inspaced parallel relationship for rotation about respective horizontalaxes, and a plurality of conicalshaped members supported on said shafts;and a hollow spherical member freely supported on said roller means forrotation thereby about an infinite number of axes.
 2. The rotationalmolding apparatus defined in claim 1, and which includes drive meanscoupled to said shafts for rotating said shafts and said conical-shapedmembers thereon at individually controllable speeds.
 3. The rotationalmolding apparatus defined in claim 1, and which includes a burnerassembly mounted in said hollow spherical member.
 4. The rotationalmolding apparatus defined in claim 3, in which said hollow sphericalmember has a multiplicity of vent holes formed therein.
 5. Therotational molding apparatus defined in claim 1, and which includes ahood surrounding said hollow spherical member, and a plurality ofnozzles mounted on said hood for directing coolant sprays onto saidhollow spherical member.
 6. The rotational molding apparatus defined inclaim 1, in which said roller means comprises first and second shaftsrotatably supported on said base in spaced and parallel relationship forrotation about respective horizontal axes; oven means surrounding saidshafts along a particular length thereof, said shafts causing saidspherical member to move through said oven means as it is rotated bysaid shafts.
 7. The rotational molding apparatus defined in claim 6, andwhich also includes a cooling chamber surrounding said shafts along aparticular length thereof, and in which said shafts cause said sphericalmember subsequently to move through said cooling chamber after passingthrough said oven means.
 8. The rotational molding apparatus defined inclaim 6, and which includes driven means coupled to said shafts forrotating said shafts at individually controllable speeds.